Fuel cells are an emerging technology because of their ability to achieve high energy efficiency and low emissions. Among the various types of fuel cells, solid oxide fuel cells (SOFCs) have emerged as one of the most promising types, because of their fuel flexibility and there efficiency. The problem with SOFCs, however is the fact that they typically operate at the very high temperature range of 600-1000°C. This greatly limits the types of materials which can be used to build up the fuel cell. Additionally, this high operating temperature results in SOFC having slow start up and cool down times.
Because they have energy densities greater than that of normal batteries, there is an interest in creating micro SOFCs which could be used in portable devices such as laptops and cellphones. In order for this to be feasible, however, the operating temperature would need to be reduced. This can be done by reducing the thickness of the functional electrolyte membrane. In light of this, work has been done on the creating of ultrathin electrolyte membranes for use in low temperature SOFCs. However, most of the work done focuses on the creation of the membrane itself, and little mention is made on how a functional fuel cell would look or how it would be assembled. Indeed most of the membranes created do not readily lend themselves to being put into a fuel cell stack.
It is believed that the transfer printing technology developed at the University of Illinois provides a solution to the problem of how to assemble µSOFCs. Transfer printing would allow the ultrathin membrane electrode assembly (MEA) to be fabricated separately, and then put into place in a fuel cell support structure. This is beneficial because it allows the complicated MEA, with its porous anode and cathode, and dense electrolyte layer, to be created independently of the fuel cell structure itself. This is much simpler than the steps which would be required to fabricate the MEA and fuel cell structure simultaneously. Additionally, transfer printing would allow the fuel cell interconnect structure to be very thin (50-100 µm), thereby allowing a very high vertical density of the stacked membranes. That is, by making both the membranes and the interconnects thinner, high density µSOFCs can be achieved.
Crackfree ultrathin (650 nm) Ni/YSZ membranes for use in µSOFCs have been successfully fabricated, and the steps taken to achieve this are presented in this thesis. Furthermore, these ultrathin Ni/YSZ membranes have been transfer printed onto a PDMS receiving substrate without incurring cracking. Although work remains to making fully functional membranes, the fact that these membranes can be transfer printed without cracking opens many possibilities for the future of solid oxide fuel cells. In light of this successful demonstration of the ability to transfer print Ni/YSZ membranes, a high power density fuel cell design based on the concept of transfer printing has been developed, and is presented with in this work.